The instant application claims priority under 35 USC 119 of Japanese Patent Application No. 2000-76370 filed on Mar. 14, 2000, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an automatic transmission loaded on a large vehicle such as a tractor-trailer.
2. Description of the Related Art
Recently, many large vehicles such as tractor-trailers, trucks and lorries are equipped with an automatic clutch and automatic transmission in order to lighten a driver""s burden. A controller associated with the automatic transmission selects a most appropriate transmission gear position in accordance with vehicle speed from a map, and the transmission is automatically shifted up and down in response to acceleration and deceleration of the vehicle.
Some of such automatic transmissions are further equipped with a manual mode which allows a driver to manually shift the transmission according to a shift lever movement. In the manual mode, unless the driver shifts the transmission with the shift lever, a current transmission gear position is maintained. The shift lever movement made by the driver only causes the transmission gear position change.
Generally, such automatic transmissions have an automatic clutch device, which automatically disengages and engages a friction clutch by an actuator.
In the manual mode, the conventional arrangement has a following problem. For example, when a vehicle is decelerated to a low speed while a relatively high speed gear is being maintained, the clutch is automatically disengaged to avoid engine stalling, and the disengaged condition is kept. After that, when an accelerator pedal is stamped to accelerate the vehicle, the clutch is automatically engaged. However, since the transmission gear position is high, the engine stalls upon clutch engagement or the clutch excessively slips. This hinders smooth driving, and damages the clutch.
An object of the present invention is to prevent an engine from stalling and a clutch from being damaged when a vehicle is accelerated after deceleration when a transmission is in a manual mode.
According to one aspect of the present invention, there is provided an automatic transmission apparatus including a controller for automatically shifting a transmission according to a gear position change signal issued from a manual shift switch. This controller (or second controller) also automatically disengages a clutch when automatic shifting takes place, and automatically engages the clutch when accelerator pedal depression exceeds a predetermined value in a clutch disengaged condition. The controller (or third controller) further decides a most appropriate gear in accordance with a current vehicle running condition, selects a higher one of the most appropriate gear and a predetermined start gear as a target gear, and shifts the transmission to the target gear regardless of the gear position change signal from the manual shift switch when the accelerator pedal depression exceeds a prescribed amount in the clutch disengaged condition, and then engages the clutch.
The most appropriate gear may be decided in a map from current accelerator pedal depression and a rotation speed of an output shaft of the transmission.
The gear position change signal may be issued from the manual shift switch in response to a shift lever movement.
The clutch may be disengaged when a rotation speed of an input shaft of the transmission drops below a value near an engine idling rotation speed.
Other objects, aspects and advantages of the present invention will become apparent to those skilled in the art to which the invention pertains from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings.